ATLAS OF PATHOLOGY

Fibroadenoma of the breast

Fibroadenoma is the most common benign breast tumor, mostly in young women. It consists in two components (epithelial and
fibroblastic), estrogen-dependent, slowly growing.

Until recently, traditionally, fibroadenoma was considered to be a benign mixed tumor, but recent studies showed that only
the fibroblastic component is neoplastic (being monoclonal), while the epithelial one is only reactive, non-neoplastic
(being policlonal).

Figure 1

Gross examination : most often it is a solitary small sized (3 - 4 cm.) nodule, well circumscribed, firm, mobile (it doesnt
infiltrate the teguments or the deep structures fat tissue or skeletal muscle) (Figure 1). On cut surface, the tumor is
white-greyish, lobulated or cauliflower-like resemblance, with a whorl-like pattern and irregularly slit-like spaces.

Microscopy : Fibroadenoma is nodular and encapsulated, included in breast. The epithelial proliferation
appears in a single terminal ductal unit and describes duct-like spaces surrounded by a fibroblastic stroma. Depending on the
proportion and the relationship between these two components, there are two main histological features : intracanalicular and
pericanalicular. Often, both types are found in the same tumor.